1. Field of the Invention
This invention relates to a light projection apparatus, in particular, an apparatus for projecting an illuminated line onto a workpiece.
2. Description of the Prior Art
In a number of industries, for example, timber sawmills, stone masonry, the textile industry, etc., frequently a requirement is to saw, grind or cut the products concerned along straight lines, which may be of considerable lengths, sometimes up to 12 meters or more.
The conventional methods of guiding the cutting machinery involved include the use of chalk lines, strips, straight edge rules and so forth. These methods are clumsy, difficult to apply and are easily displaced by the operations in progress.
More recently, the use of lasers projecting a long thin line of light on the workpiece have come into use. This system represents a major improvement over the older conventional methods. However, a disadvantage of existing laser systems, particularly where very long lines are required, is that the intensity of the light is greatly reduced towards the far end of the projected line, and this, combined with the unavoidable small angle of incidence of the bream on to the workpiece at the far area, makes if difficult to distinguish the line clearly.
The known art utilizes a lens system comprising a solid cylindrical glass rod to fan out the rays of a laser beam to produce a line of laser light on the surface of the object when the beam is projected on to such an object.
In FIG. 1, curve C1 shows the comparative intensities of the light produced by this system at different angles emanating from the light source. As can be seen, the intensity is greatest over the center portion of the beam (at x), gradually reducing to zero towards the outer ends of the beam.
FIG. 2 shows a typical layout of an arrangement for projecting a line of light AB, from laser 1, on to a workpiece. Curve C2 shows the comparative brightness resulting at various points along this line. As can be seen, bright illumination is provided on the portion of the line nearer to the light source, while on the portion further from the source the level of illumination is substantially lower. This is accounted for by a combination of factors, each of which materially contributes to this unsatisfactory situation.
The factors are:
1. The greater distance from the light source. PA1 2. The comparatively lower intensity of light emanating from the lens in the outer portion of the beam. PA1 3. The very oblique angle at which the light strikes the surface of the workpiece at this end of the line, resulting in an already reduced relative light intensity being spread over a long length of the line.
A device sometimes employed to improve this result is to offset the solid cylindrical lens from the center line of the laser beam. This results in a higher proportion of light being projected from the lens to one side of the beam as compared with the other side. Curve D in FIG. 1 illustrates the comparative light intensities obtained with such a prior art device in which the beam from the light source is offset from the axis of the lens used to deflect the beam onto the work surface. This effect is utilized to increase to some extent, the portion of light transmitted to the more distant portion of the line. However, even with this modification, the variation in illumination of the line from one end to the other is considerable.
DE 43 20 177 discloses a light projection apparatus which is used to project an illuminated line onto a surface. The disclosed apparatus utilizes a laser source to emitting a laser beam. A specially shaped prism receives the emitted laser beam and refracts it in such a way as to produce a fanned beam which forms a line of light on the surface. There is a generally constant intensity of illumination in the line of light.
Apart from the difficulties of manufacturing the specially shaped prism to achieve the desired refraction, the disclosed apparatus has the disadvantage that it the fanned laser beam is projected symmetrically onto the surface about an axis at right angles to the surface. This makes it unsuitable from projecting rather long illuminated lines onto the surface, because the longer the line, the further away from the surface the laser projection apparatus must be situated.
Therefore, in light of the deficiencies of the prior art, it is an object of the invention to provide a system in which a line of laser light may be projected on to a surface situated obliquely relative to the light source, such a line of light being substantially evenly illuminated throughout its length, and thus more easily visible at all points along its length.